Decking a Block
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Racer
Joined: Jan 2000
Posts: 334
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Decking a Block
I have a 427 "351" block (2-bolt main) that I am going to rebuild and I have some questions before I start:
1. I do not want to deck it if I do not have to. I would like to preserve the stamping if at all possible. This block has never been decked and has the correct broach marks and stamping. I am told that many machine shops do this as a matter of course unless told otherwise, in which case many will not do the work. Under what conditions is decking a requirement?
2. What is the criteris for reboring the cylinders vs. honing. I assume that there will be some sort of a ridge at the top of the cylinder wall that indicates amount of wear and this ridge can be removed without having to bebore the block. Is it possible / wise to rebore a block without decking it.
3. Is there anything special or unique about these 351 blocks that I need to take into consideration before I get started? I recall reading something about grooves in cam bearing for oiling or something being mentioned here before.
4. Are there any parts I should spend $ on to upgrade vs. using the General's originals, e.g., oil pump, rods, bearings, etc.? I understand a lot of people buy parts from Paragon for these engines. Are they the best place to buy pistons, bearings, etc. from.
5. Finally, is there a reference or references that I should be reading before I start ?
1. I do not want to deck it if I do not have to. I would like to preserve the stamping if at all possible. This block has never been decked and has the correct broach marks and stamping. I am told that many machine shops do this as a matter of course unless told otherwise, in which case many will not do the work. Under what conditions is decking a requirement?
2. What is the criteris for reboring the cylinders vs. honing. I assume that there will be some sort of a ridge at the top of the cylinder wall that indicates amount of wear and this ridge can be removed without having to bebore the block. Is it possible / wise to rebore a block without decking it.
3. Is there anything special or unique about these 351 blocks that I need to take into consideration before I get started? I recall reading something about grooves in cam bearing for oiling or something being mentioned here before.
4. Are there any parts I should spend $ on to upgrade vs. using the General's originals, e.g., oil pump, rods, bearings, etc.? I understand a lot of people buy parts from Paragon for these engines. Are they the best place to buy pistons, bearings, etc. from.
5. Finally, is there a reference or references that I should be reading before I start ?
Melting Slicks
Joined: Aug 1999
Posts: 2,848
Likes: 3
From: Atlanta, Ga, Fulton
Re: Decking a Block (clearrun)
1. I have rebuilt a lot of engines and NEVER decked a used block. If the engine was blowing head gaskers or the deck surface is not flat then it needs decking. A good mac=hine shop will put a straight edge on the deck and see what amount of warpage exists not just start decking it for the heck of it.
This is one of those things that ( in my opinion) should be reserved for blueprinted race engines if of course your deck surface is in good shape. I don't think this is something that is necessary on every engine that is rebuilt. It is not necessarily bad, just not necessary every time.
2. Have the shop check the bore sizes and roundness of the bores. If they are worn beyond certain max sizes any rings you put in will wear prematurely and the piston clearances will be too large. To much clearance means noise and premature wear as well as oil buring. The cylinders have to be round within defined limits and the assembeled clearance has to be correctly adjusted for the type of piston (forged or cast or hyperutectic) you are planning to run. Honing a block as opposed to boring might be OK depends on the condition of the cyls. Honing instead of boring can also be a cheap low bucks way to build a short lived engine.
3. I guess that a 351 block is an early big block? I don't pay much attention to the numbers but if the block used a grooved rear cam journal you gotta have a grooved cam as a replacement. Use the correct cam bearing and cam and you are done with this topic. If you can't find the cam grind you want with a groove in it a copmpetent machine shop can duplicate the groove using a stock grooved cam as a pattern.
4. The Generals stuff is usually the best to use. For my money the aftermarker hot rod goodie stuff has caused as much grief as satisfaction. Generally speaking (no pun intended) the GM stuff is as good as it gets for street use, likely it is the best. Think about it! MILLIONS of engines were produced with GM parts and almost all survived a lot of abuse and lack of maint. Go with GM and you likely will be glad you did. A point: parts suppliers like TRW are OEM suppliers to GM and you likely can pay more going thru GM parts division than thru a TRW parts supplier. Sealed Power and TRW were somehow related in the past but I don't know about now so there is another parts source that I think was an OEM for GM. I once took a GM crate moto apart and the pistons had TRW partnumbers right on the piston head.
[Modified by TheOman, 11:13 AM 8/28/2002]
This is one of those things that ( in my opinion) should be reserved for blueprinted race engines if of course your deck surface is in good shape. I don't think this is something that is necessary on every engine that is rebuilt. It is not necessarily bad, just not necessary every time.
2. Have the shop check the bore sizes and roundness of the bores. If they are worn beyond certain max sizes any rings you put in will wear prematurely and the piston clearances will be too large. To much clearance means noise and premature wear as well as oil buring. The cylinders have to be round within defined limits and the assembeled clearance has to be correctly adjusted for the type of piston (forged or cast or hyperutectic) you are planning to run. Honing a block as opposed to boring might be OK depends on the condition of the cyls. Honing instead of boring can also be a cheap low bucks way to build a short lived engine.
3. I guess that a 351 block is an early big block? I don't pay much attention to the numbers but if the block used a grooved rear cam journal you gotta have a grooved cam as a replacement. Use the correct cam bearing and cam and you are done with this topic. If you can't find the cam grind you want with a groove in it a copmpetent machine shop can duplicate the groove using a stock grooved cam as a pattern.
4. The Generals stuff is usually the best to use. For my money the aftermarker hot rod goodie stuff has caused as much grief as satisfaction. Generally speaking (no pun intended) the GM stuff is as good as it gets for street use, likely it is the best. Think about it! MILLIONS of engines were produced with GM parts and almost all survived a lot of abuse and lack of maint. Go with GM and you likely will be glad you did. A point: parts suppliers like TRW are OEM suppliers to GM and you likely can pay more going thru GM parts division than thru a TRW parts supplier. Sealed Power and TRW were somehow related in the past but I don't know about now so there is another parts source that I think was an OEM for GM. I once took a GM crate moto apart and the pistons had TRW partnumbers right on the piston head.
[Modified by TheOman, 11:13 AM 8/28/2002]
Drifting
Joined: Aug 2000
Posts: 1,805
Likes: 36
From: Annapolis MD
Re: Decking a Block (clearrun)
1. You should not have to deck a block unless you either want to change the piston/deck dimensions (pistons "usually" sit some dimension below the deck); or the decks are not flat and are experiencing head gasket sealing problems. I have had several (more than I wanted to) BBC motors machined at a local (Rt 4 and DC beltway) machine shop. E-mail me if you want their phone.
2. If there is any decernable ridge you will need to bore the engine (and get new pistons) to be able to correctly set the piston/wall clearances. You "might" be able to just home the block if it is really low milage. Cast piston clearances are on the order of 0.0015 inches, so any ridge you can actually see is going to be too much. Boring machines index the block from the crank journals not the deck, so decking or not should have no effect on the ability to bore the block.
3. Some early block need a groved cam bearing. I don't know off hand which, but if the block has the groved bearing it must be replaced with the same.
4. Always replace rod and main bolts. And, as long as your replacing them, I'd use ARP high strength wave-lock rod bolts. Since BBC head bolts go into the water jackets they will also usualy need to be replaced (corrosion on the ends). Be carefull if you use ARP head bolts, as with the required washers the head is higher and may hit on your exhaust (most header flanges require gridning the head of the bolt thinner and notching the flange for clearance). Use a heavy duty oil pump drive shaft, but the stock oil pump (get a new one and check the clearances) is usually adequate.
-Greg
2. If there is any decernable ridge you will need to bore the engine (and get new pistons) to be able to correctly set the piston/wall clearances. You "might" be able to just home the block if it is really low milage. Cast piston clearances are on the order of 0.0015 inches, so any ridge you can actually see is going to be too much. Boring machines index the block from the crank journals not the deck, so decking or not should have no effect on the ability to bore the block.
3. Some early block need a groved cam bearing. I don't know off hand which, but if the block has the groved bearing it must be replaced with the same.
4. Always replace rod and main bolts. And, as long as your replacing them, I'd use ARP high strength wave-lock rod bolts. Since BBC head bolts go into the water jackets they will also usualy need to be replaced (corrosion on the ends). Be carefull if you use ARP head bolts, as with the required washers the head is higher and may hit on your exhaust (most header flanges require gridning the head of the bolt thinner and notching the flange for clearance). Use a heavy duty oil pump drive shaft, but the stock oil pump (get a new one and check the clearances) is usually adequate.
-Greg
